# 1???????
list = [12,3,4,55]
# 2???????
list.insert(0,31)
print(list)
# 3??????list
list.extend([5,6,7])
# 4????????
print(list[0])
# 5?????????
print(list[-1])
print(list[len(list)-1])
# 6?????31
print(list.index(31))